S. Tokumitsu

Surface induced state on ZrC(111): Angle-resolved photoemission study

Abstract Angle-resolved photoemission spectroscopy (ARPES) has been used to study the electronic structure of a ZrC 0.9 (1 1 1) surface. A sharp emission is observed at just below the Fermi level in normal emission spectra. This peak is ascribed to the emission from a surface induced state formed through charge redistribution around the surface. The two-dimensional dispersion of the state is found to be small.

Adsorption of K on NbC(100): photoemission and thermal desorption study

Abstract The adsorption state of K on NbC(100) has been studied with core-level photoemission spectroscopy (CLPES) and thermal desorption spectroscopy (TDS). The adsorption mechanism of K on the NbC(100) surface is found to be very unique as compared with those of many alkali-metal surface systems. The TDS study shows that the desorption energy of K increases with the increase of K coverage ( θ K ). The work function measurements show that the polarization of the NbC(100) surface after K adsorption is small as compared with those for many alkali-metal surface systems. The lineshape analysis of the K 3p photoemission spectra shows that the valence electronic density of states for adsorbed K is nearly independent on the coverage. Considering these results, it is proposed that the K-adsorbed layer is grown via the island formation mechanism.

Angle-resolved photoemission study of the surface electronic structure of TaC(111)

Abstract Angle-resolved photoemission spectroscopy utilizing synchrotron radiation has been used to study the electronic structure of the TaC0.95(111) surface. A strong emission from a surface induced state is found just below the Fermi level in the normal-emission spectra. Resonant photoemission study shows that the state is derived from Ta 5d orbitals. The two-dimensional band structure for the surface electronic state of the TaC(111) is mapped in a surface Brillouin zone using off-normal-emission spectra. The electronic structure of the surface is found to be very similar to those of NbC(111) and TiC(111) surfaces, though some surface induced states, which are not found for NbC(111) and TiC(111) surfaces, are newly found.

Interaction of hydrogen with ZrC(111) surface: angle-resolved photoemission study

Abstract Angle-resolved photoemission spectroscopy (ARPES) utilizing synchrotron radiation has been applied to study the adsorption of hydrogen on a ZrC(111) surface at room temperature. The electronic structure of the ZrC(111) clean surface is characterized by a surface-induced state at around the Fermi level. Hydrogen adsorption attenuates the surface-induced state and induces a H 1s-induced split-off state at 6.5 eV at the \ qG point, at saturation coverage. The two-dimensional electronic structure of the H saturated surface is investigated by off-normal-emission measurements and the H 1s-induced state is found to have a dispersion of (1 × 1) periodicity. The bandwidth of this state is determined to be 1.0∼1.2 eV, which correlates well with those of metal-H adsorption systems.

Potassium adsorption on the polar NbC(111) surface: core-level photoemission study

Abstract The potassium adsorption process on a NbC(111) surface has been studied with core-level photoemission spectroscopy. The coverage dependence of the work function and the K 3p core-level photoemission spectrum reflects that adsorption proceeds via a polarization-depolarization phase transition, which is brought about up to a coverage of 0.3 ML. A spectral line-shape analysis for the K 3p core-level peak has been performed, and it is proposed that the interaction between the K 4s orbital and the substrate Nb 4d orbitals plays an important role in the initial stage to form the polarized K overlayer.

Electronic structure of the nitride layers formed on a Si(111) surface: angle-resolved photoemission study

Angle-resolved photoemission spectroscopy utilizing synchrotron radiation has been applied to study the electronic structure of the nitride overlayers formed on a Si(111) surface. As the Si(111) surface exposed to NO at saturation coverage is heated to 900°C, the (8 × 8)-N overlayer is formed. The NZnpπ non-bonding, N 2px,y + Si 3p bonding, and Si 3s-derived bonding bands are identified in the ARPE spectra using the polarization-dependent measurements. As the surface is further heated to 1050°C, the (8 × 8)-N overlayer is changed to the quadruplet-N overlayer, however, the spectral profile for the quadruplet-N overlayer is similar to that for the (8 × 8)-N overlayer. The effect of the “surface umklapp” process arising from the lattice mismatch between nitride overlayers and Si(111) (1 × 1) substrate are investigated with off-normal-emission measurements.

Cs adsorption on a polar NbC(111) surface : photoemission and Auger electron spectroscopy studies

The Cs adsorption process on a NbC(111) surface has been studied with core-level photoemission spectroscopy (PES) and Auger electron spectroscopy (AES). Coverage-dependent Cs 4d core-level PES shows that the polarization-depolarization transition of the Cs overlayer occurs in the coverage region of 0.5 ≤ θ ≤ 0.8 ML where the work function shows a minimum value. The charge transfer in the initial stage of adsorption is investigated using valence-related AES, and it is found that the transfer of the Cs 6s charge to the substrate occurs in the polarized phase.

Angle-resolved photoemission study of the clean and oxygen-covered NbC(110) surface

Abstract Angle-resolved photoemission spectroscopy utilizing synchrotron radiation has been used to study the electronic structure of a NbC0.95(110) clean surface and the surface exposed to oxygen at room temperature. The spectra for the clean surface show that the bulk band emissions show small hv-dependent dispersions at hv = 27.5–65 eV, thus the density of state effect is dominant in the photoemission process at this photon energy range. A surface state is found to be formed on this surface at 1.7 eV at the \ gG point. The state is attributed to a Tamm state pulled off from the Σ3 bulk band. As the oxygen is adsorbed on the (110) surface, the O 2p-derived states are formed at 4.7 and 6.5 eV for 5–10 L exposure. The inner valence C 2s band emission is strongly affected by oxygen adsorption, indicating that the oxygen atom sits on the surface carbon atoms.

Theoretical study of the valence photoelectron spectrum for nitride films on Si(111) surface

Abstract to determine the position of nitrogen atoms in nitride films on Si(111) surface, a discrete-variational (DV)-X α calculation was performed to simulate the observed valence band photoemission spectrum for the (8 × 8) and the quadruplet phase. For the (8 × 8) phase, the model of Nishijima et al. ( SiN = 1.80 A , ∠SiNSi = 101°) was found to be appropriate. We propose a new model with SiN = 1.9–2.0 A and ∠SiNSi = 99–93° or the quadruplet phase.